645739091 has 2 divisors, whose sum is σ = 645739092. Its totient is φ = 645739090.

The previous prime is 645739079. The next prime is 645739109. The reversal of 645739091 is 190937546.

Together with next prime (645739109) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-645739091 is a prime.

It is not a weakly prime, because it can be changed into another prime (645739051) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322869545 + 322869546.

It is an arithmetic number, because the mean of its divisors is an integer number (322869546).

Almost surely, 2^645739091 is an apocalyptic number.

645739091 is a deficient number, since it is larger than the sum of its proper divisors (1).

645739091 is an equidigital number, since it uses as much as digits as its factorization.

645739091 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 204120, while the sum is 44.

The square root of 645739091 is about 25411.3968722697. The cubic root of 645739091 is about 864.3421512065.

The spelling of 645739091 in words is "six hundred forty-five million, seven hundred thirty-nine thousand, ninety-one".